Additive for increasing efficiency in thermal hydrodealkylation



United States Patent 3,442,967 ADDITIVE FOR INCREASING EFFICIENCY INTHERMAL HYDRODEALKYLATION Donald J. Wynnemer, Baytown, Tex., assignor toEsso Research and Engineering Company No Drawing. Filed June 14, 1968,Ser. No. 736,965 Int. Cl. C07c 3/30, 3/58 US. Cl. 260-672 11 ClaimsABSTRACT OF THE DISCLOSURE The thermal dealkylation of polyalkylaromatic hydrocarbons (having from 1 to 3 carbon atoms in each alkylsubstituent) is increased by the addition of a radicalforming compoundchosen from the group consisting of the C to C alkanols. Theradical-forming compound may be added to the hydrodealkylation zone inamounts from about 20 to about'1000 mols per million mols of aromatichydrocarbon introduced into the hydrodealkylation zone. In thehydrodealkylation of dimethyl naphthalene, the addition of 200 p.p.m. ofethanol was found to increase the once-through conversion from 44.3% to99.5%, with the production of naphthalene increased from 5.5% to-19.1%and theproduction of monomethyl naphthalene increased from 23.5% to72.1%, based on feedstock.

Discussion of the invention The present invention relates to thehydrodealkylation of alkylated aromatic compounds. More particularly,the present invention relates to the use of a radical-forming additivewhich increases the efliciency of the hydrodealkylation process,particularly in the treatment of di(C to C )alkyl aromatic hydrocarbons.In its most specific aspects, the present invention deals with theaddition of 20 to 1000 (preferably about 200) mols of a C to C alkanolper million mols of a dimethyl naphthalene.

The thermal hydrodealkylation of aromatic compounds is well known in theart. An exemplary thermal hydrodealkylation process is carried out inthe presence of hydrogen at pressures from about 400 p.s.i.a. to about800 p.s.i.a. and at temperatures from about 1000 F. to about 1600" F.Hydrogen is added to the dealkylation zone at a treat rate from about7,000 s.c.f./b. of feedstock to about 15,000 s.c.f./b. of feedstock. Thecontact time during which the feedstock is present in the dealkylationzone may range from 5 to 40 seconds.

The present invention relates to the dealkylation of poly(C to C )alkylaromatic hydrocarbons, such as polymethyl benzenes, methyl-ethylbenzenes, and polymethyl naphthalenes. Exemplary of the polymethylbenzenes are the xylenes, the isomeric trimethyl benzenes, isomerictetramethyl benzenes, and mellitene. Exemplary of the polymethylnaphthalenes are the isomeric di-, triand tetramethyl naphthalenes. TheC to C alkyl substituents may also be mixed, such as1,5-methyl-3-ethylbenzene. The present invention has been demonstratedto be particularly effective in the dealkylation of dimethyl naphthalenesuch as 1,2-, 1,3- and 1,6-dimethyl naphthalene. The invention may beused in the dealkylation of substantially pure hydrocarbons, or instreams containing mixtures of the polyalkyl aromatic hydrocarbons.

The radical-forming additive of the present invention is a C to Calkanol, with ethanol being preferred. The additive may be added to thehydrodealkylation zone in amounts ranging from 20 to 1000 mols ofadditive per million mols of aromatic hydrocarbon being introduced intothe hydrodealkylation zone. The upper limit is set by economics; morecould be used if desired. Preferably, when ethanol is being used in thedealkylation of dimethyl 3,442,967 Patented May 6, 1969 naphthalenes,about 200 mols of ethanol will be added per million mols of the dimethylnaphthalene.

In order to illustrate the present invention, examples are givenhereinbelow which compare the dealkylation reaction when carried out inthe absence of radical-forming additives with the performance whenethanol is added and with the addition of a well-known radical-formingadditive, t-butyl peroxide. As will be seen, the ethanol additive isconsiderably more effective than t-butyl peroxide and is extremelyeffective as compared to the reaction carried out in the absence ofadditives.

Examples Examples 1, 2 and 3 were carried out in a laboratorydealkylation reactor constructed as follows. The main components otherthan the reactor were a liquid feed pump, a hydrogen metering device,product quench and collecting system, and a tail gas metering andsampling system. The reactor was a 1-inch Schedule stainless steel pipe30 inches long and was heated in a fluidized sand bath. In each one ofthe runs a technical mixture of dimethyl naphthalenes was introducedinto the reaction zone at a temperature of 1200 F., and at a rate givingthe contact time which is shown below in the table. The hydrogen treatrate in each case was obtained by adding heated hydrogen into thereaction zone in admixture with the dimethyl naphthalene feedstock. Inthose cases where the additives were employed, the additives were addedto the dimethyl naphthalene feedstocks before introduction to thereaction zone.

By reference to the preceding table, it is seen that thehydrodealkylation reaction carried out in the absence of promotersprovided a conversion of 44.3 mol percent. The use of t-butyl peroxideincreased the conversion only to 49.6 mol percent. However, ethanolprovided a substantially complete reaction, with 99.5% of the dimethylnaphthalenes in the feedstock having disappeared in a once-throughprocess. Note also that the ethanol additive provided a high selectivityto monomethyl naphthalene. In those cases where monomethyl naphthaleneis desired as a product, the once-through reaction can be carried outand a preponderantly monomethyl naphthalene product can be recovered bydistillation. If, however, naphthalene is the desired product, thehydrodealkylation reaction can be carried out by recycling themonomethyl naphthalene into the hydrodealkylation zone until it has beenconverted to naphthalene. Note that 19.1 weight percent naphthalene wasproduced on a once-through basis with the use of ethyl alcohol ascompared to 5.5 weight percent when no additive was employed and only8.1% when t-butyl peroxide was employed.

Thus, it is shown that the ethanol additive of the present inventionsubstantially increases the conversion and selectivity of thehydrodealkylation reaction.

Having disclosed my invention and a preferred mode of carrying it out(in Example 3), what is to be covered by Letters Patent should begoverned not by the specific examples herein given, but rather only bythe appended claims.

I claim:

1. In the thermal hydrodealkylation of poly(C to C )alkyl aromatichydrocarbons, the improvement of adding to the hydrodealkylation zonefrom 20 to 1000 mols of a C to C alkanol per million mols of aromatichydrocarbon.

2. A process in accordance with claim 1 wherein the aromatic hydrocarbonis a polymethyl naphthalene.

3. A process in accordance with claim 1 wherein the alkanol is ethanol.

4. A process in accordance with claim 2 wherein the alkanol is ethanol.

5. A process in accordance with claim 1 wherein the aromatic hydrocarbonis dimethyl naphthalene and the alkanol is ethanol.

6. A process in accordance with claim 5 wherein the ethanol is added atthe rate of about 200 mols per million mols of dimethyl naphthalene.

7. A method for thermally hydrodealkylating a C to C polymethylnaphthalene which comprises in a hydrodealkylation zone contacting saidpolymethyl naphthalene in the vapor phase at a temperature from 1100 to1300 F.,

a pressure from 500 to 700 p.s.i.g., and a residence time from 5 to 40seconds with molecular hydrogen at a rate of 7,000 to 15,000

s.c.f. of hydrogen per barrel of polymethyl naphthalene 4 while addingto said hydrodealkylation zone from about 20 to about 1000 mols of a Cto C alkanol per million mols of polymethyl naphthalene.

8. A method in accordance with claim 7 wherein the alkanol is ethanol.

9. A method in accordance with claim 8 wherein the polymethylnaphthalene is dimethyl naphthalene.

10. A method in accordance with claim 9 wherein the ethanol additionrate is about 200 mols per million mols of dimethyl naphthalene.

11. A method in accordance with claim 10 wherein the hydrodealkylationconditions are:

a temperature of about 1200 F.,

a pressure of about 600 p.s.i.g.,

a H treat of about 15,000 s.c.f. of hydrogen per barrel of dimethylnaphthalene, and

a residence time of about 13.8 seconds.

References Cited UNITED STATES PATENTS 3,110,745 11/1963 Peck et a1.260672 3,178,485 4/1965 Myers 260-672 DELBERT E. GANTZ, PrimaryExaminer.

G. E. SCHMITKONS, Assistant Examiner.

